1. Field of Invention
The present invention relates to a variable valve apparatus. More particularly, the present invention relates to a hydraulic pressure valve apparatus.
2. Description of Related Art
An internal combustion engine generates power by burning fuel in a combustion chamber in air media drawn into the chamber. Intake valves are operated by a camshaft in order to intake the air, and the air is drawn into the combustion chamber while the intake valves are open. In addition, exhaust valves are operated by the camshaft, and a combustion gas is exhausted from the combustion chamber while the exhaust valves are open.
An optimal operation of the intake valves and the exhaust valves depends on a rotation speed of the engine. That is, an optimal lift or optimal opening/closing timing of the valves depends on the rotation speed of the engine. In order to achieve such an optimal valve operation depending on the rotation speed of the engine, various research has been undertaken. For example, a valve for driving a valve is designed having different shapes, a variable valve lift apparatus has variable different lifts depending on an engine speed and so on.
However, since a CVVL (continuous variable valve lift apparatus) which is controlled mechanically, uses a link, eccentric cam a control shaft and so on, so that moment of inertia and accumulated clearance is relatively large, and development of dynamic characteristic of a valve is limited.
Also, each valve is controlled by the same camshaft simultaneously, realizing valve lift is limited.
For overcoming the drawbacks, an electric-hydraulic pressure variable lift apparatus has been developed.
FIG. 7 is a graph showing a valve profile and oil pressure of a conventional electric-hydraulic pressure variable valve apparatus.
Referring to FIG. 7, when a valve is opened, a piston may not descend smoothly due to resistance. That is, as shown in the graph, hydraulic pressure peak is generated as well as noise is generated.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.